What are Default Methods in Interfaces (Java 8+ / C# 8+)? Why were they introduced?
Default Interface Methods
Default interface methods allow an interface to provide an implementation for a method instead of requiring every implementing class to define it. Java introduced default methods in Java 8 primarily to evolve existing interfaces without breaking all existing implementations. C# introduced default interface implementations in C# 8 for a similar API-evolution and compatibility purpose. They should be used carefully because putting substantial business logic into interfaces can blur responsibilities.
- 1
Default methods provide reusable interface behavior.
- 2
They allow interfaces to evolve without immediately breaking every implementation.
- 3
Java introduced them in Java 8.
- 4
C# supports default interface implementations from C# 8.
- 5
Conflicting defaults may require explicit resolution depending on the language.
- 6
Default methods should not become a dumping ground for complex business logic.
Follow-up Questions
- What happens if two interfaces provide the same default method?
- Can a default method access instance state?
- Why were default methods introduced in Java 8?
- How do default interface implementations work in C#?